This invention relates generally to fittings used to seal a section of pipe during a hot tapping operation or where a sealed connection is needed. More specifically, the invention relates to fittings for use in pipe and pipeline applications in which a high integrity seal is required or in a high pressure, high temperature, or highly corrosive environment (or some combination of the three).
In the typical hot tapping application, such as that used in the petroleum industry, a fitting is welded on the exterior of a pipe that has flowing gas or liquid under pressure. The fitting includes a flange on its outlet connection side and a hot tapping machine is secured to the flange. By use of highly specialized equipment, a hole can then be drilled through the wall of the pipe while gas or liquid continues to flow in the pipe. This access hole or opening can be used to insert equipment which temporarily blocks flow through the pipe while repairs are being made to the pipe. After the repairs are complete, the equipment is removed but the opening that provides communication to the interior of the pipe needs to be closed. Preferably the closure is made in such a way that at some future date access can be again obtained through the fitting to the interior of the pipe.
In certain applications, the elastomeric seals used to seal between the clamp and the pipe may not be ideal because of a high pressure, high temperature, or highly corrosive environment (or some combination of the three). Here, the use of a metal seal might be desirable. For the purpose of this disclosure, high pressure is defined as 1500 psi and above. High temperature is 75° C. and above. Highly corrosive means an environment which is likely to effect the integrity of an elastomeric seal and for which a super alloy material is better suited.
The use of metal C-seal rings is well known in industrial or plant applications but is not known or used in sealing hot tap fittings to pipes. The application of metal C-seal rings to pipelines is not straightforward because the seals are “flat” and not “double curved” like those needed in a pipeline application. Additionally, the pipe surface itself—even if it were flat—does not lend itself to a metal seal. The pipe surface is typically coated with a protective coating and might have other surface irregularities or defects that pose a challenge to maintaining a proper seal.